Primary-aged children infected with the coronavirus had much lower viral loads than adults with Covid-19, a study found.
Viral load – the amount of virus that a person harbors – is considered by some scientists to be associated with increased transmissibility, although there are debates about these claims.
Data from public health officials in the Netherlands show a 16-fold difference in the amount of virus between those over 80 and children under 12 years.
Rapid antigen tests, such as the 15-minute display used in schools and airports, are also likely to be less accurate for children than adults because of their smaller load, the researchers say.
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This graph shows the Cp value for coronavirus patients by age. Cp is a measure of how many cycles of PCR analysis, which amplified a genetic signal, are required to detect a SARS-CoV-2 signal. The higher the number, the lower the virus load. ‘The mean Cp values between the oldest (> 79 years) and the youngest (<12 years) population differed by more than 4 PCR cycles, indicating a 16-fold difference in viral load,' the researchers write .
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More than a quarter of a million people in North Holland were tested between 1 January 2020 and 1 December 2020.
Of these, 211,933 were done by qualified health professionals, with viral load data available for 18,290.
All these swabs were processed by the same regional laboratory in the Netherlands to ensure that the tests were processed and analyzed in the same way.
“To our knowledge, this is the first study to evaluate SARS-CoV-2 virus burden distributions in a large number of patients from different patient categories,” write the researchers in their study, which has not yet been peer-reviewed and published online. as pre-print.
“Our data show a clear association between age and SARS-CoV-2 viral load, with children (less than 12 years old) showing lower viral loads, regardless of gender and symptom duration.”
More than 2,500 of the people tested were younger than 20 and 238 of them were younger than 12, which is equal to primary school age.
One measure used to quantify viral load is Cp, which indicates how many cycles of PCR – repeating and amplifying genetic material – are required before the virus can be detected.
The higher the figure, the lower the virus load, as it indicates how many amplification cycles are required.
In the study, the researchers note that the difference between the mean Cp figure for older than 80 and under 12 years is more than four cycles, which is equivalent to a 16-fold increase.
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“The most remarkable finding of this study was the association between SARS-CoV-2 viral load and age, with significantly lower viral load in children,” add the study authors from Kennemerland in the north of the Netherlands.
“As previous studies have suggested that young children play a limited role in SARS-CoV-2 transmission, our data support this suggestion.”
During the pandemic, there was a mystery surrounding the fact that children are relatively unaffected by Covid-19, when adults are so badly affected.
Children have far fewer cases during the entire coronavirus pandemic than for other respiratory diseases, including influenza.
The main theory for this is due to how the coronavirus invades human cells via a receptor called ACE2 which is found in many cells in the upper respiratory tract.
Consequently, Professor Wendy Barclay of Imperial College London, a member of NERVTAG, explained last month that it makes adults ‘easy targets’ compared to children.
This is because the amount of ACE2 that a person expresses increases naturally and gradually over time, with young children having very few people.
ACE2 is the receptor on the surface of human cells that kills and uses the coronavirus to infect it.
The Dutch researchers point out that antigen tests, which are faster but not as reliable as PCR tests, are even less accurate when used by an infected patient with a low viral load.
In infected children under 12 years of age, the registered viral load in almost a third (31.1 percent) of the cases was less than 30, almost double the proportion of people with this low reading in all other age groups.
As a result, the researchers say that ‘SARS-CoV-2 antigen tests may have a lower sensitivity in children than in adults’.